For increasing crop production and better appearance of crops, farmers usually spray a great deal of pesticide on crops to protect them from attacks by insect pests. Currently, organophosphate pesticides and carbamate pesticides have replaced organochlorine pesticides, thereby becoming the most widely used pesticides as a consequence of low bioaccumulation and high biodegradability. In spite of the advantages mentioned above, organophosphate pesticides and carbamate pesticides still result in residues building up in the soil, crops, surface water and industrial wastewater, causing considerable threats to human health and the natural environment in the case of heavy use. Particularly, both of the above-mentioned pesticides are neurotoxins. Once one of them enters into an organism, it will inhibit activity of acetylcholine esterase by irreversibly binding to the active site thereof so as to slow down hydrolysis rate of acetylcholine and interfere neural transmission. Depending on the toxicity, dosage and duration of contact of the pesticide itself, such pesticides have resulted in different symptoms such as fatigue, nausea, sleepiness, blurry vision and even death. Thus, countries around the world have paid close attention to control such nerve inhibiting pesticides. Fairly strict regulatory standards, especially on pesticide involved in drinking water, food and industrial wastewater, have been imposed.
The conventional methods of pesticide residue analysis, especially for pesticide residues in vegetables and fruits, include spectrophotometry, nuclear magnetic resonance spectroscopy, thin layer chromatography, atomic absorption spectroscopy, gas chromatograpy, liquid chromatography, fluorimetry and so on, among which gas chromatograpy and liquid chromatography are more commonly used due to advantages of favorable repeatability, sensitivity, and capability of determining pesticide type and concentration. However, such methods have to be executed by following standard detection steps as well as by laboratory technicians equipped with the expertise conducting sample pretreatment and performing analysis via instrumental operation in order to obtain valid detection results. Thus, conventional detection of pesticide residues can not be applied to a large quantity of agricultural products rapidly and conveniently. In recent years, several methods for detecting enzyme inhibiting pesticides by means of biochemical reaction and electrochemistry technique have been developed. For example, U.S. Pat. No. 6,406,876 (Gordon et al.) has disclosed an immobilized enzyme technology without making a huge amount of solution. However, drawbacks of immobilized enzyme include high cost, complicated manufacturing process and stringent preservation conditions. Thus, analysis should be performed by professionals. Both TW patent M376764 and CN patent CN101082599 (Lin et al.) have disclosed a simpler and more convenient method of immobilizing enzyme on the analytical apparatus to detect pesticide residue concentration. However, the design approach is more complicated in which enzyme and related reactant have to be stored respectively in the electrodes and sample containers so that two-phase reactions are proceeded respectively, likely to result analysis errors. Besides, TW patent 1301541 (Wu et al.) has disclosed a method for immobilizing enzyme on the electrode to determine pesticide concentration in aqueous solution via the degree of enzyme inhibition caused by pesticides. However, the method of immobilizing enzyme is more complicated. Mass production is difficult. Moreover, the quantitative method of pesticide residue concentration is simply presented by the rate of enzyme inhibition, thereby making a user who operates the apparatus unable to figure out clearly the actual amount of pesticide residue.
In view of the above reasons, it is necessary to propose a simple and innovative analytical apparatus devised to minimize the measurement errors in concentration of pesticide residues in a more simple design approach. Moreover, a user who is not equipped with the expertise can detect pesticide residue concentration in a rapid and convenient manner and immediately gain a practical understanding of the amount of pesticide residue.